my shins and calves hurt about 5 minutes into it? I thought it was because I didn't stretch enough, but today I could only do about 5 minutes at a time and then I had to go stretch again? They don't do that if I'm just walking on the ground.

Could be your shoes. What type of shoes are you wearing? Do you have a serious running store near where you live? There is one near me that when I go they watch me run/walk to see what type of shoe would suite me best. They don't really let you pick out what you'd like.......they tell you what you should be wearing for optimum results.